This invention relates to video display systems, and more particularly to an apparatus for the on-line verification of the functionality of the various subsystems within the video display system.
In existing video display systems which include logic such as raster scan logic, counters, video memories, and shift registers, verification of the system while still on-line is accomplished by displaying a test pattern for the user to examine and left for the user to observe the test pattern and conclude that everything is functioning properly if the test pattern conforms to the expected display. This technique has worked whenever the user is looking for something wrong, but the first drawback is that the user has to think something is wrong. The present invention takes the user out of the loop for determining if something is wrong and verifies that the system is functioning properly on-line without interfering with the information being displayed, and without intervention by the user.